Polyelectrolyte cement

ABSTRACT

The invention relates to a single-component or multiple-component polyelectrolyte cement containing at least two reaction partners: 
     (a) at least one metal-cation-releasing compound and 
     (b) one or more polyelectrolytes capable of being converted into a solid state, wherein at least one of the polyelectrolytes is at least partially water soluble, and wherein at least a part of the reaction partner (a) and/or (b) is coated with an organic surface-coating agent. 
     In one preferred embodiment, at least one part of the formulation constituents of the cement is present in granulated form, wherein at least a part of the reaction partner (b) serves as an essential granulation agent. The polyelectrolyte cement is particularly stable in storage and can be easily mixed.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/EP00/02855 which has an Internationalfiling date of Mar. 31, 2000, which designated the United States ofAmerica and was not published in English.

The invention relates to a single-component or multiple-componentpolyelectrolyte cement containing at least two reaction partners, (a) ametal-cation-releasing compound and (b) one or more polyelectrolytescapable of being converted into a solid state, wherein at least one ofthe polyelectrolytes is at least partially water soluble, and wherein atleast one part of reaction partner (a) and/or (b) is coated with anorganic surface coating agent. Moreover, the invention relates to agranulate obtained from at least one part of the formulationconstituents of the polyelectrolyte cement present in solid form,wherein, in the context of an autogenous granulation process, at leastone part of reaction partner (b) serves as the essential granulationagent, and the granulate disintegrates back to the primary grain oncontact with the liquid formulation constituents.

Furthermore, the invention relates to processes for production of thegranulate and the use of the polyelectrolyte cement as a dentalmaterial.

In the sense of the present invention, polyelectrolytes are understoodto be polymers with ionically dissociable groups, which may be acomponent or a substituent of the polymer chain and of which the numberis so great that the polymers are at least partially water soluble atleast in their partially dissociated form. In the sense of the presentinvention, polyelectrolyte cements are understood to be materials whichcontain a polyelectrolyte. In particular, these polyelectrolytes shouldbe able to react with a metal-ion-releasing compound in the context of achelate-forming reaction, particularly preferably, an acid-basereaction/neutralization reaction. This reaction is described as a curingreaction or simply as curing. A polymerization reaction may also takeplace alongside this curing, if polymerizable compounds are addedtogether with initiators suitable for the polymerization of thesecompounds.

Polyelectrolyte cements of this kind are obtained, for example, throughthe reaction of a polyalkenoic acid, in particular a polyacrylic acid,with zinc oxide or a metal-cation-releasing, so-called basic glasspowder in the presence of water. These cements have been known since1967 as polycarboxylic cements [D. C. Smith, Biomaterials 19, 467-478(1998)] and since 1969 as (conventional) glass-ionomer cements(glass-polyalkenoate cements, GIC) [A. D. Wilson, B. E. Kent, DE 20 61513]. Polyelectrolyte cements which contain additional polymerizablecompounds and suitable initiators are, for example, syntheticallymodified glass-ionomer cements (see e.g. R. Mathis, I. L. Ferracane, J.Dent. Res. 66, 113 (Abstract 51) (1987)] or compomers [see e.g. EP 219058].

The above named polyelectrolyte cements can be formulated astwo-component paste-paste systems and single-component paste systems.Normally, however, the above-named polyelectrolyte cements areformulated as powder-liquid systems. In this context, thepolyelectrolyte may be either in the liquid, or it may be mixed with thepowder as a solid. Mixed forms, in which parts of the polyelectrolyteare contained in the powder and parts in the liquid, are also known[see, for example, GB-A-17880-72, DE-A-2319715]. Solid mixtures, inwhich at least one part of the polyelectrolyte is present alongside ametal-cation-releasing compound, are defined as “dry powder mixtures”.

Addition of polyelectrolytes to the powder as a solid is advantageous,for example, if additional processing time is to be gained by thedissolution of the polyelectrolyte or if the complete amount ofpolyelectrolyte in the solution leads to a high, and therefore no longersuitable viscosity and workability.

One disadvantage of the dry powder mixture is that in the presence ofmoisture, e.g. from atmospheric humidity during the storage of theproduct up to the time of use, a reaction takes place between the tworeaction partners, i.e. the metal-cation-releasing compound and thepolyelectrolyte, which slows down the curing of the cement. This meansthat a reliable use of the polyelectrolyte cement is no longerguaranteed, because the curing of the material increases in dependenceupon the duration of storage.

This plays an important role, in particular with the hand-mixed variantsof these polyelectrolyte cements, because these products are conceivedfor the cost-conscious user in such a manner that several applicationscan be implemented with the packaged material. Accordingly, the drypowder mixture is provided in small glass containers which allow accessto atmospheric moisture every time the material is removed, which slowsdown the curing. Moreover, in time, it becomes more difficult to mix thecement because, as a result of the reaction occurring at the surfacebetween the metal-cation-releasing compound and the polyelectrolyte inthe presence of atmospheric humidity, agglomerates of increased soliditymay be formed and can only be broken down with an increased input ofenergy during mixing.

It is possible to achieve stable curing throughout the storage period bypreventing the access of moisture to the dry powder mixture. This canonly be realized through more elaborate packaging: for example,polyelectrolyte cements of this kind which are offered in a mixingcapsule specially developed for single application, are blister-packedin aluminium foil possibly with an additional dessicant pad. Indeed,this measure does have the desired stabilizing effect on curing, but isassociated with significantly increased cost of manufacture which istherefore transferred to the consumer. Moreover, with increasingawareness of environmental matters, the consumer's acceptance of anelaborately packaged product is constantly declining.

Also, particular steps must be taken during production and packaging ofthe dry powder mixture in order to minimize contact with atmosphericmoisture as much as possible, otherwise initial damage to the dry powdermixture may occur and this may cause difficulties with the packaging ofthe dry powder mixture which leads to increased expenditure onmaintenance.

Another option for protecting substances essentially from environmentalinfluences is to provide the substances to be protected with a coating.

Organic coating compounds used in the production of tablets [H. P.Fiedler, Lexicon der Hilfsstoffe für Pharmazie, Kosmetik und angrenzendeGebiete (Dictionary of excipients for pharmaceutical, cosmetics andassociated areas) Editio Cantor Verlag Aulendorf, 4^(th) edition, 1996,pages 1498-1500] are known in the pharmaceutical industry. Depending onthe area of use of the tablet, these coating compounds may be soluble inacid (solubility in the stomach), soluble in alkali (solubility in theintestine) or soluble in water. Typical representatives of these verywidely used tablet coatings are the Eudragit® types manufactured byRöhm. Eudragit® L (acid-resistant) is an acid-functional polymer, whileEudragit® E (acid soluble) provides amino groups [H. P. Fiedler, Lexiconder Hilfsstoffe für Pharmazie, Kosmetik und angrenzende Gebiete(Dictionary of excipients for pharmaceutical, cosmetics and associatedareas) Editio Cantor Verlag Aulendorf, 4^(th) edition, 1996, pages596-598]. The product Copolymer 845 manufactured by ISP, which providestertiary amino and pyrrolidon groups, is also amino-functional, however,water soluble. Coating compounds based on cellulose derivatives (such asOPADRY® II, manufactured by Colorcon, or Sepifilm, manufactured bySeppic) are also known. Copolymers, which also contain polysaccharides,such as e.g. Surelease (by Colorcon) are also used for this purpose (seeproduct catalogues of the individual companies).

The manufacturers provide recommendations regarding the film thicknessrequired to achieve resistance to moisture with these coating compounds.For example, Röhm recommends film thicknesses of approximately 10 μm forthe production of moisture-resistant tablet coatings; this correspondsto around one milligram of coating compound per cm² (Eudragit® productcatalogue by Röhm). To achieve the recommended film thickness on thefinely ground constituents of the powder in a polyelectrolyte cement(specific surface of approximately 3 m² per gram), this would have to becoated with approximately 30 grams of coating compound per gram ofpowder.

This represents a substantial intervention into the composition of thepolyelectrolyte cement. It must be regarded as particularly important inthis context that the materials named for surface coating arenon-reactive additives with reference to a polyelectrolyte cementreaction. Even earlier experiments have repeatedly shown that in thecase of polyelectrolyte cements, non-reactive additives generally leadto a significant deterioration of properties even in concentrations of afew percent; this applies in particular with reference to mechanicalvalues such as compression strength or bending strength.

DE 3610844 and DE 3610845 describe surface coating agents for dentalcements based on calcium aluminate. By contrast with polyelectrolytecements, these cure through hydration rather than through chelateformation or neutralization. Since these cements cure in a basic medium,without the participation of an acid, the requirements for acidresistance of the coating agent are not comparable with the requirementsplaced on a polyelectrolyte cement. The polymers used for surfacecoating in these documents are only water soluble and are also used inconcentrations up to 10% as thickeners in the aqueous reaction solutionwhich is used for hydration.

The object of the present invention is therefore to provide apolyelectrolyte cement which can be readily produced, filled intocontainers and mixed, and which is so stable with regard to moisturethat neither its properties nor its curing are altered within theframework of normal storage conditions. If possible, this should beachieved without the need for special packaging technology and withoutany reduction in the mechanical values such as compression strength andbending strength.

According to the invention, this object is resolved by asingle-component or multiple-component polyelectrolyte cement and/or agranulate as described in the patent claims.

Surprisingly, by contrast with the polyelectrolyte cements known fromthe state of the art, a surface coating of at least a part of themetal-cation-releasing compound and/or of the polyelectrolyte allows theproduction of a polyelectrolyte cement which is so stable in respect ofatmospheric moisture that neither its curing nor properties are changedwithin the context of normal storage conditions; accordingly, itsusefulness is not negatively influenced and the mechanical values arecomparable with those of polyelectrolyte cements known from the state ofthe art.

Moreover, surprisingly, the tackiness of the polyelectrolyte cement tothe processing instrument is reduced and the curing transition isadvantageously shortened.

Characteristic of the surface coating materials according to theinvention is that these are film-forming materials which are depositedonto the surface of a solid core (reactive component of thepolyelectrolyte cement), which afterwards at least partially cover thiscore without entering into a fixed chemical bond with this core. Withinthe framework of the polyelectrolyte cement reaction, the surfacecoating agents can preferably be separated from the core, but duringstorage, they protect the core from the influence of moisture.

Reactive materials, which form a chemical bond with the surface of thereactive components of the polyelectrolyte cement (e.g. silanizationagents as described in DE 3941629, DE 19526224 or DE 19605272) are notsurface coating agents in the sense of this invention.

Film-forming materials which are already used as coating materials inthe pharmaceutical industry because of their toxicological safety (seeabove) are preferred. Polymeric film-forming materials, in particularthose with a molar mass greater than 10,000 are particularly preferred.In this context, polymers which provide an adequately high solubility inthe aqueous acidic medium so that they release the reactive componentsufficiently quickly and in this manner prevent the occurrence of anysignificant retardation of the curing reaction are particularlypreferred. Preferably, the retardation should not exceed 1 minute,particularly preferably the retardation should not exceed 30 seconds.

This requirement is in contradiction to the requirement for an effectiveprotection from moisture. Surprisingly, it was found that per se knownfilm-forming materials, which are used for film-coated tablets in athickness of 40-200 μm, also fulfil this requirement, if they areapplied to the reactive component of a polyelectrolyte cement in aconcentration of less than 3%, preferably less than 2% and particularlypreferably less than 1% (relative to the weight of the polyelectrolytecement).

As a result of the large specific surface of the components, which iswithin the range 0.2 to 10, preferably 0.5 to 5, particularly preferably1 to 3 m²/g, this corresponds to a film thickness of only a few nm andis therefore smaller by a factor of 1000 to 50000 than is normal in thepharmaceutical industry. To guarantee the high level of solubility,tablet coating agents which are soluble in gastric juices are preferred;polymers containing amino-functional comonomers are particularlypreferred.

These polymers can be used both as such and also in a neutralized orpartially neutralized form. Any acids may be used for theneutralization. However, organic acids are preferred, and carboxylicacids are particularly preferred, in particular acids which are known tobe used in polyelectrolyte cements, such as hydroxycarboxylic acids, inparticular, tartaric acid or citric acid.

Surprisingly, it has been shown that significantly thinner coatings thanthose recommended by the pharmaceutical industry for organic coatingsubstances used in the production of tablets are sufficient to resolvethe object of the invention. Even coatings in the range 0.01 to 3 wt.-%,preferably 0.1 to 2% and very particularly preferably 0.2 to 1.5 wt.-%,lead to stable systems. Within this concentration range, the materialsused for the coating are not critical with reference to the otherproperties of the cement. The named percentage values relate to thetotal weight of the surface-coated material.

In the drawings there are shown in:

FIG. 1 a graphic representation of the processing and storage times ofglass coated with Eudragit® (examples 2 to 7) by comparison with anuncoated glass (Example 1),

FIG. 2 a graphic representation of the processing and storage times ofglass coated with other coating agents (Examples 8 to 10) by comparisonwith an uncoated glass (Example 1)

FIG. 3 a graphic representation of the processing and storage times ofzinc oxide coated with Eudragit® (Example 12) by comparison with anuncoated zinc oxide (Example 11).

Polyelectrolyte cements may be formulated as single-component ormultiple-component cements. This means that the component of thepolyelectrolyte cement may be provided separately packed in one or morecomponents of the cement. This is necessary if individual reactionpartners must be stored separately from one another because the reactionotherwise occurring between them would negatively influence the storagestability of the polyelectrolyte cement. For example, the three reactionpartners in glass ionomer cements (GIC), the basic glass powder, thepolyalkenoic acid and water, must be stored separately from one anotherin such a manner that no reaction occurs. Glass ionomers are thereforeoffered in at least two components: one component can contain the basicglass powder and the polyalkenoic acid and the second component cancontain the water. The polyalkenoic acid may also be partially orcompletely in the water. Curing begins after the mixing of the twocomponents. A storage stability problem regarding a reaction betweenthese two reaction partners is probable only if the two reactionpartners (a) and (b) are present at least partially in both reactioncomponents. Then, according to the invention, it is advantageous if atleast one part of the reaction partners found in the same component (a)and/or (b) is coated with an organic surface coating agent.

Water is required as a reaction partner so that curing can take place.The quantity required may very considerably depending upon the reactionpartners. It is also possible for the polyelectrolyte cement accordingto the invention to contain no water itself, but for the water requiredfor the reaction to originate from the surroundings, e.g. the patient'smouth. This occurs, for example, with the material class of theabove-mentioned compomers. Since curing between the two reactionpartners (a) and (b) does not take place without water, light-curingcompomers, for instance, can also be formulated as single-componentcements. In this case, the reaction between the metal-cation-releasingcompound and the reaction partner (b), is, like the quantity of water(from the patient's mouth), of subordinate importance by comparison withthe polymerization reaction which occurs here additionally through theaddition of polymerizable compounds together with the initiatorsappropriate for the polymerization of these compounds.

The polyelectrolyte cements according to the invention contain 0-30wt.-% water, preferably 0-25 wt.-% water. The compomers generallycontain no water or no significant amounts of water. Glass ionomercements modified with synthetics preferably contain 3-12 wt.-% water,particularly preferably 5-10 wt.-% water. Glass ionomer cements andpolycarboxylic acid cements contain particularly preferably 5-25 wt.-%water. For example, a GIC contains 5-20 wt.-% water, preferably 8-15wt.-% water. Unless otherwise specified, the named percentages by weightrelate, in each case, to the total weight of the polyelectrolyte cement.

In the sense of the present invention, metal-cation-releasing compoundshould be understood to refer to all substances which are capable ofreleasing metal cations, which can then react with reaction partner (b)in the sense of a chelate forming reaction. In this context, the cationsreleased should preferably be multivalent, particularly preferablydivalent and trivalent. Compounds of this kind are produced for thepolyelectrolyte cement in a powdered form of a particle size normal forpolyelectrolyte cements [see, for example, DE-A-2061513].

Examples of metal-cation-releasing compounds are metal salts, inparticular metal oxides and metal hydroxides, particularly preferablyfrom the group of earth alkaline metals, such as, e.g. CaO, MgO,Ca(OH)₂, Mg(OH)₂, and ZnO, certain finely dispersed metals, such asfinely dispersed zinc etc. (U.S. Pat. No. 3,028,247), and basic glasspowders, which are particularly suitable through their proportion ofdivalent and trivalent ions, such as, Ca²⁺, Sr²⁺, Ba²⁺, La²⁺, Y³⁺, Al³⁺,in the presence of water for reaction with reaction partner (b) (see,for example, DE-A-2061513, EP-A-0023013, EP-A-02 41 277). Furtherexamples are metal-cation-releasing silicates, such as e.g. sheetsilicates, such as montmorillonites, bentonites or calcium silicates,zirconium silicates, sodium aluminium silicates, and zeoliths, includingthe molecular sieves.

The polyelectrolyte cement according to the invention contains themetal-cation-releasing compound preferably in a proportion of 15 to 85wt.-%, particularly preferably 18 to 80 wt.-% and very particularlypreferably 50 to 70 wt.-% relative to the total composition.

The polyelectrolyte (b) used according to the present invention is apolymer with ionically dissociable groups, which may be substituents ofthe polymer chain and whose number is so great that the polymers, atleast in their (partially) dissociated form, are at least partiallywater soluble. Substituents such as —COOH, —OH, —PO(OH)₂, —OPO(OH)₂,—SO₂(OH) are particularly suitable in this context. Organic polyacids(DE-A-2061513), such as polymers and copolymers of acrylic acid,methacrylic acid (EP-A-0 024 056), itaconic acid, maleic acid,citraconic acid, phosphonic acid (EP-A-0340 016; GB-A-22 91 060) areparticularly preferred. Alongside these, if several polyelectrolytes arepresent, water-insoluble polyelectrolytes may also be present in thepolyelectrolyte cement. The prerequisite is merely that at least one ofthe polyelectrolytes according to the above definition must be at leastpartially water soluble.

In the sense of the present invention, “capable of conversion into asolid state” should be understood as meaning that the polyelectrolyte iseither per se a solid at room temperature or at least is a solid in itspartially or completely dissociated form.

The polyelectrolytes should be able to react with themetal-cation-releasing powder component in the context of achelate-forming reaction, preferably an acid-basereaction/neutralization reaction.

Other polyelectrolytes which are not capable of conversion into a solidstate may also be present in the polyelectrolyte cement, but separatelyfrom the metal-cation-releasing compound in another component of thepolyelectrolyte cement according to the invention, which willconsequently be a multi-component cement.

The polyelectrolyte cement according to the invention contains the atleast partially water-soluble polyelectrolytes which are capable ofbeing converted into a solid state preferably in a proportion from 0.5to 30 wt.-%, particularly preferably 2 to 25 wt.-% and very particularlypreferably 5 to 20 wt.-%.

According to the invention, at least one part of reaction partner (a)and/or (b) is surface coated with an organic surface coating agent. Theorganic coating substances known in the pharmaceutical industry whichare also used for the production of tablets can be used for this purpose(see above).

The surface coating can be implemented with very different materials andmethods. Preferably, polymeric compounds are used. For instance, sugarsolutions, polyacrylates, methacrylates, solutions based on gum arabic,gelatines, methylcellulose, other cellulose derivatives or polyethyleneglycols can be used (see Ullmanns Encyklopädie der technischen Chemie,Verlag Chemie, Weinheim, 4^(th) edition, 1979, pages 18-155ff; H. P.Fiedler, Lexicon der Hilfsstoffe für Pharmazie, Kosmetik und angrenzendeGebiete (Dictionary of excipients for pharmaceutical, cosmetics andassociated areas) Editio Cantor Verlag Aulendorf, 4^(th) edition, 1996,pages 1498-1500]. The particularly preferred organic surface coatingagent is an at least partially acid-soluble surface coating agent. Thevery particularly preferred organic surface coating agents are thesurface coating agents soluble in gastric juices including their salts.For instance, polymers with amino groups (such as Eudragit® Emanufactured by Röhm), which can be used both in their amine form andalso in a neutralized form, neutralized e.g. with tartaric acid (seebelow), are particularly suitable as coating materials. Also, polymermaterials based on polysaccharides, such as OPADRY®, or based oncellulose derivatives, such as Surelease or Sepifilm, lead to equallygood results.

Important representatives of these product classes are shown in thefollowing table. These materials may serve as examples for surfacecoating agents in the sense of the invention.

TABLE Film-forming agents used as surface coating agents Type Filmformer Molar mass Lit. Natural Shellac (excretion of the Approx. 10001,2,3,4 film-formers Indian Lac) Mastix (pistachio resin) 1,3 Sandarac(resin of Callitris 1,3 quadrivalvis) Tolubalsam (resin of 1,3 Myroxylonbalsamum) Dammar resin (cat eye 1,3 resin, resin of the dammar tree)Benzoe resin (Asiatic 1,3 resin) Keratin (eg. from 40,000-70,000 1,2,3feathers) Maizin (Zein) (protein from 10,000-22,000 1,3 maize seeds) GumArabic 2 Gelatines 2 Semi-synthetic Gelatines treated with 1,3film-formers formaldehyde Salol (acetaldehyde- 1,3 phenol-condensate)Cellulose Cellulose acetate 40,000 2,2a,4 derivatives phthalateHydroxyethyl cellulose 2,4 Methyl cellulose 20,000-150,000 4Hydroxypropyl methyl 10,000-150,000 2a,4 cellulose Hydroxypropylcellulose 60,000-1,200,000 4 Sodium-carboxymethyl 80,000-600,000 4cellulose Ethyl cellulose (e.g. 4,7 Surelease-Colorcon)Hydroxypropylmethyl 20,000 4 cellulose phthalate Poly(meth) Copolymersof methacrylic 150,000 (Eudragit 2,4,5,6 acrylates esters and amino- E)functional methacrylates 800,000 (Eudragit (e.g. Eudragit E - Röhm,E30D) Copolymer 845 - ISP) Copolymers of 135,000 (Eudragit 2,4,5(meth)acrylic acid and L or S) methymethacrylate (e.g. 150,000 (EudragitEudragit L, Eudragit S, RL or RS) Eudragit RL, Eudragit RS- 250,000(Eudragit Röhm) L30D) Vinyl Polyvinyl pyrrolidon 10,000-350,000 2a,4polymers Polyvinyl acetate phthalate 25,000-40,000 4 Mixtures e.g.hydroxypropyl- and 8 hydroxypropyl- methylcellulose (e.g.Spifilm-Seppic) e.g. hydroxypropyl 7 cellulose and polysaccharides (e.gOpadry II - Colorcon 1. F. Gstirner, Grundstoffe und Verfahren derArzneibereitung, Ferdinand Enke Verlag, Stuttgart, 1960, page 529 ff 2.P. H. List et al., Arzneformenlehre, 4^(th) edition, WissenschaftlicheVerlagsgesellschaft mbH, Stuttgart, 1985, page 127 ff 2a. ibid page 5403. Römpp Chemie Lexikon, 9^(th) edition, Georg Thieme Verlag, Stuttgart,New York, 1995 4. K. H. Bauer, K.-H. Frömming, C. Führer,Pharmazeutische Technologie, 3^(rd) edition, Georg Thieme Verlag,Stuttgant, New York, 1991 page 341 ff. 5. H. P. Fiedler Lexikon derHilfsstoffe, Editio Cantor Verlag Aulendorf, 1996 6. ISP, Brochure 7.Colorcon, Brochure 8. Seppic, Brochure

Since most of the surface coating agents described in the literature areonly adequately soluble for the surface coating in organic solvents, thenormal precautions for protection from explosions must be implementedwhen handling organic solvents. This can be simplified by converting thesurface coating agent into a water-soluble form.

This can be achieved through conventional measures such as introducingpolar or ionic groups into the surface coating agent. The neutralizationof acidic or basic groups is particularly suitable in this context. Forexample, Eudragit® E can be converted into an adequately water-solubleEudragit® E salt, e.g. its tartrate, for the surface coating, so thatexplosion precautions can be dispensed with during the surface coatingbecause exclusively water may be used as a solvent for the surfacecoating.

The surface coating can be implemented in accordance with the methodsdescribed in the literature. Without limiting the invention in thiscontext, some processes will be referred to briefly below by way ofexample.

Initially, the solids to be coated are mixed to a pulpy consistency withthe surface coating agent dissolved in an appropriate solvent and thenhomogenized in an appropriate appliance with vigorous shearing. Thepossible mixing appliances include, for example, kneaders or varioustypes of mixer. Finally, the surface coated material is dried andoptionally sieved.

The polyelectrolyte cement may provide the usual accelerators orretarders. Examples of accelerators are short-chained, organic acids,such as acetic acid, alcohols such as ethyl alcohol, salts such as zincacetate. Examples of retarders are organic triols such as glycerine,some organic amino alcohols such as triethanolamine (U.S. Pat. No.3,028,247).

In the case of glass ionomer cements, the addition of chelate formers toadjust the appropriate curing process is of particular importance(DE-A-23 19 715). Numerous compounds are possible in this context,primarily those which contain the hydroxy or carboxyl groups whichprovide the chelate formations or both. Particularly outstanding resultswere achieved with tartaric acid or citric acid, in particular with acontent of 5 wt.-%. The addition of a metal chelate also shows thedesired effect.

In the sense of the present invention, the polyelectrolyte cementsaccording to the invention contain 0 to 10, preferably 0 to 5 wt.-% of acompound of this kind, preferably tartaric acid.

Moreover, the curing rate can be adjusted by treating the surface of themetal-cation-releasing compound. For example, the curing rate of glassionomer cements can be influenced by tempering the basic glass [ClinicalMaterials 12, 113-115 (1993)] or by the duration of the surfacetreatment of the basic glass with acid [DE-A-29 29 121]. Alongside thiscuring reaction, an additional polymerization reaction may also takeplace in the polyelectrolyte cement according to the invention, ifpolymerizable compounds and suitable initiators for the polymerizationof these compounds are added.

A polymerizable compound in the above sense should be understood in thiscontext as a compound which can enter into a polymerization reaction.Compounds of this kind may for example, carry additional substituentswhich can react with the metal-cation-releasing compound, such as —COOHgroups. To ensure compatibility with the hydrophilic matrix formedthrough the curing reaction system, comprising the reaction partners (a)and (b), it is preferable if the polymerizable compounds are of ahydrophilic character. Examples of the compound capable ofpolymerization and/or curing used in the present context are:

(i) ethylenically-unsaturated compounds:

Vinyl, vinyl ether, acrylate, methacrylate compounds, which may alsocontain hydroxy groups among other groups; acrylates and methacrylates,such as methyl(meth)acrylate, n- or i-propyl(meth)acrylate, n-, i- ortert.-butyl(meth)acrylate and hydroxyalkyl(meth)acrylate,di(meth)acrylates of propandiol, butandiol, hexandiol, octandiol,nonandiol, decandiol and eicosandiol, di(meth)acrylates of ethyleneglycol, diethylene glycol; esters of (meth)acrylic acid, such astriethylene glycol dimethacrylate; urethan(meth)acrylic acid; α-cyanoacrylic acid; crotonic acid, cinnamic acid; sorbinic acid;(meth)acrylamides such as butyl vinyl ether; mono-N-vinyl compounds suchas N-vinylpyrrolidon. Diacrylic and dimethacrylic esters of bishydroxymethyltricyclo(5.2.1.0^(2.6))-decan;2,2-bis-b(3-methacryloxy-2-hydroxypropoxy)phenylpropane (bis-GMA);3,6-dioxa-octamethylenedimethacrylate (TEDMA);7,7,9-trimethyl-4,13-dioxo-3,14,-dioxa-5,12-diazahexadecan-1,16-dioxy-dimethacylate(UDMA);

(ii) Epoxides of the general formula

 in which the symbols are as follows:

Z denotes an aliphatic, cycloaliphatic or aromatic radical with 0 to 22C-atoms or a combination of these radicals, wherein one or more C-atomscan be substituted by O, C═O, —O(C═)—, SiR₂ and/or NR and wherein R isan aliphatic radical with 1 to 7 C-atoms, wherein one or more C-atomscan be substituted by O, C═O and/or —(C═O)—.

A denotes an aliphatic, cycloaliphatic or aromatic radical with 1 to 18C-atoms or a combination of these radicals, wherein one or more C-atomscan be substituted by O, C═O, —O(C═)—, SiR₂ and/or NR, wherein R is analiphatic radical with 1 to 7 C-atoms, in which one or more C-atoms canbe substituted by O, C═O and/or —(C═O)—.

B₁, B₂, D, E denote independently of one another a H atom or analiphatic radical with 1 to 9 C-atoms, wherein one or more C-atoms canbe substituted by O, C═O, —O(C═)—, SiR₂ and/or NR and wherein R is analiphatic radical with 1 to 7 C-atoms, wherein one or more C-atoms canbe substituted by O, C═O and/or —(C═O)—,

n denotes 2 to 7

m denotes 1 to 10

p denotes 1 to 5

q denotes 1 to 5 and

X denotes CH₂, S or O;

These compounds and possibilities for their production are described inDE-A-196 48 283 or WO 95/30402.

Epoxides of the general formula

 wherein

A, A′ denote independently from one another an unbranched or branchedaliphatic, cycloaliphatic or aromatic radical with 0 to 13 C-atoms or acombination of these radicals, wherein one or more C-atoms can besubstituted by O, C═O, O(C═O), Si, N, S,

B1, B1′, B2, B2′ denote independently of one another H, an unbranched orbranched aliphatic, cycloaliphatic or aromatic radical with 0 to 6C-atoms or a combination of these radicals, wherein one or more C-atomscan be substituted by O, (C═O), O(C═O), Si, N, S,

F, F′ denote independently of one another an unbranched or branchedaliphatic, cycloaliphatic or aromatic radical with 0 to 10 C-atoms or acombination of these radicals, wherein one or more C-atoms can besubstituted by O, (C═O), O(C═O), Si, N, S,

D denotes an unbranched or branched aliphatic, cycloaliphatic oraromatic radical with 1 to 15 C-atoms or a combination of theseradicals, wherein at least one C-atom is replaced by SiGG′, SiG or Siand one or more C-atoms can be substituted by O, (C═O), O(C═O), N or S,

G, G′ denote independently of one another an unbranched or branchedaliphatic, cycloaliphatic or aromatic radical with 0 to 8 C-atoms or acombination of these radicals, wherein one or more C-atoms can besubstituted by O, (C═O), O(C═O), Si, N, S,

n and m denote independently of one another 0, 1, 2 or 3 and n+mprovides 2 to 6,

and wherein the molar mass of the epoxide or the average molar mass ofthe mixture of epoxides is 250 to 1000 g/mol.

These molecules and the processes for their production are described inthe German patent application (Sipox).

(iii) monomers polymerizable by ring-opening metathesis or polymers withthe following structure:

M—A_(n)

wherein M is equivalent to H or a linear, branched, cyclic or polycyclicorganic or metallo-organic radical. Organic radicals may beC₁-C₃₀-alkyl, C₆-C₂₀-aryl, C₇-C₃₀-alkaryl or C₃-C₃₀-cycloalkyl with 0-10heteroatoms from the group N, O, Si, P, S and a number of n linkagepoints for A. Metallo-organic radicals contain, in addition to theabove-named organic radicals, additional linear, branched, cyclic orpolycyclic lattices of an inorganic nature.

Preferred M groups may be

subject to the condition that Q is equal to O, S, SO₂ or a linear,branched or cyclic C₁-C₂₀-alkylene radical, which can also befluorinated; m is an integer from 1-20; T is a linear, branched orcyclic saturated or unsaturated C₁-C₂₀-hydrocarbon radical and q is aninteger from 3-20.

A is an unsaturated cyclic or polycyclic organic radical of the generalformula

C—D,

wherein C is equal to H or a linear, branched or cyclic saturated orunsaturated organic C₁-C₂₀-radical with 0-10 heteroatoms from the groupN, O, Si, P, S and 0-10 carbonyl groups and D is a cyclobutenyl-,cyclopentenyl radical or a radical unsaturated at the designatedposition and optionally additionally at another position in the ringsystem of the general formula

in which the symbols have the following meanings:

R¹, R², R³ denote H or a linear branched or cyclic saturated orunsaturated organic C₁-C₂₀ radicals with 0-10 heteroatoms of the groupN, O, Si, P, S and 0-10 carbonyl groups, and

X denotes O, NH, S or a saturated or unsaturated C₁-C₃₀ hydrocarbonradical.

The ring-opening metathesis-polymerization is also described in theliterature (Comprehensive Polymer Sci.; 4; pages 109-142).

The polymerizable compounds may be contained in the polyelectrolytecements according to the invention in proportions of 0 to 30 wt.-%,preferably 0 to 20 wt.-% and in the compomers and synthetically modifiedglass ionomer cements for example in proportions of 7 to 15 wt.-%.

If required, catalysts for hot, cold and/or light polymerization may beadded as initiators. In this context, peroxides such as dibenzoylperoxide, dilauryl peroxide, tert.-butyl peroctoate or tert.-butylperbenzoate, but also α,α′azobis(isobutyroethyl ester), benzpinacol and2.2′-dimethylbenzpinacol may be used. As photoinitiators, all substanceswhich trigger polymerization after irradiation with UV and/or visiblelight may be used. These include, for example, diazonium compounds (U.S.Pat. No. 3,205,157), sulfonium compounds (U.S. Pat. No. 4,173,476)iodonium compounds (U.S. Pat. No. 4,264,703, U.S. Pat. No. 4,394,403) orbisacylphosphinoxides (EP-A-184095). Other photoinitiators are e.g.α-diketones, such as preferably 9, 10-phenantrenquinone, diacetyl,furil, anisil, 4,4′-dichlorbenzil, 4,4′-dialkoxybenzil andcampherquinone. Initiators for cationic light curing are e.g. thecompounds described in DE-A-197 36 471. Further cationic polymerizationinitiators are described in DE-A-25 15 593 and in WO 96/13538. Theknown, radical-providing initiator systems based on peroxide/amine orperoxide/sulfituric- and/or barbituric acid, such as benzoyl or laurylperoxide with NN-dimethyl-sym.-xylidine and NN-dimethyl-p-toluidine, areprimarily suitable for cold polymerization.

Catalysts which can be added for polymerization after ring-openingmetathesis are, for example, radical or cation formers and the compoundsdescribed in WO 96/23829 or the compounds described by van der Schaaf,Hafner, Mühlebach in “Angewandte Chemie” [Applied Chemistry] 1996, 108pages 1974-1977.

Normal accelerators for the polymerization reaction, which may be added,are for, example, oxidative additives such as hydroperoxides (e.g. cumolhydroperoxide, dialkyl peroxides), peresters (e.g. tert.-butylperbenzoate, tert.-butyl isononanoate) or inorganic oxidation agents(e.g. potassium persulfate, sodium perborate) or other radical-producingadditives, such as diaryliodinium compounds, aromatic amines,alkylamines or aromatic alkylamines.

The initiators, catalysts and accelerators etc. described in the aboveparagraph may be contained in the polyelectrolyte cements according tothe invention in proportions of 0-1 wt.-%.

Moreover, the polyelectrolyte cement according to the invention maycontain excipients such as colourings, pigments, x-ray contrast agents,flow-enhancers, thixotropy agents, polymeric thickening agents orstabilizers. The normal fillers for dental materials are, for exampleglass and quartz powder, pyrogenic, highly dispersed silicic acids andmixtures of these components. These other additives are contained in thepolyelectrolyte cements of the invention in proportions of 0-60 wt.-%.

The named fillers may also be hydrophobized, for example, by treatmentwith organosilanes or -siloxanes or by etherification of hydroxyl groupsto alkoxy groups.

In one particular embodiment, at least one part of the components of thepolyelectrolyte cement present in solid form may be presented inpowdered, granulated and/or tablet form.

Granulates are understood to be sedimented accumulations of granulategrains. A granulate grain is an asymmetric aggregate or agglomeratecemented together without providing a harmonious, geometric form, madefrom powder or dust particles, which generally have better flowproperties than powder mixtures (Ullmanns Encyklopädie der technischenChemie, Verlag Chemie, Weinheim, 4^(th) edition, 1979, 18-157ff]. Thesurface of the grain, which may be spherical, rod-shaped or cylindrical,is uneven and ridged. [H. P. Fiedler, Lexicon der Hilfsstoffe fürPharmazie, Kosmetik und angrenzende Gebiete (Dictionary of excipientsfor pharmaceutical, cosmetics and associated areas) Editio Cantor VerlagAulendorf, 4^(th) edition, 1996, page 722]

With reference to the practical handling of powders, granulation offersmany advantages over the finely dispersed condition of products in theform of fine powders of dusts. In particular polluting the atmospherethrough dust emissions, a defined flow-behaviour, simpler handlingduring production and packaging and also quicker dispersal ordissolution considerably improve the handling of products of this kind[Rumpf, Chemie-Ingenieur-Technik 30 and 46].

To cause finely dispersed powders to form into granulates, forces ofadhesion are required between the individual grains. The adhesive forcesmay be derived, for example, from solid bridges such as sintering,chemical reaction, curing binding agents or through crystallizationbetween the individual particles. Further possibilities for binding areprovided by interfacial forces on freely-moving liquid surfaces,adhesion and cohesion forces, forces of attraction between solidparticles and interlocking bonds.

In the pharmaceutical industry, so-called “adhesive granulation” iswidespread. The granulates obtained are either used per se or arefurther processed to make tablets. In the context of adhesivegranulation, similar compounds are used as binding agents (adhesives,granulation excipients) as are used in the production of film coatings.Alongside the compounds named in the table, the following may also beused: gelatines, starch, alginates (F. Gstirner, Grundstoffe undVerfahren der Arzneibereitung, Ferdinand Enke Verlag, Stuttgart, 1960,pages 25 ff; P.H. List et al. Arzneiformlehre, 4^(th) edition,Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, 1985, page 84 ff].

If the polyelectrolyte cements according to the invention are presentedin the form of powder-liquid systems, mixing is often very difficult,because the powders have extremely large surface areas (see above) whichmake mixing very troublesome. Moreover, with the high powder-liquidratio often required for good mechanical values, a large quantity ofpowder is often used with a small amount of liquid. The mixing processis made more difficult by the relatively small volume of liquid comparedwith the particle volume and the high specific surface of the cementwhich is to be wetted.

When granulation is used, the wetting of the powder with the liquid canbe accelerated, because with granulation, the powder is combinedinternally resulting in porous structures. Through this structure, theliquid is taken up into the granulate more rapidly because of capillaryforces, which considerably reduces the mixing time.

The use of granulates for dental applications has already been describedin JP-06321724, JP-A-53023190, DE-A-35 11 721. DE-A-35 11 721, whichdescribes the granulation of alginate impression compounds, describesthe granulation excipients, without which granulation would not bepossible. Moreover, these granulated materials are not the at leastpartially surface-coated material in accordance with the presentinvention.

Granulation excipients, which are normally used for production of theparticle cluster, cannot be used in the systems according to theinvention, because the quantity required for this would negativelyinfluence the physical properties of the cured polyelectrolyte cement,in particular the curing reaction (see above).

For example, Eudragit® E is used in the pharmaceutical industry as acurrently available granulation excipient because of its adhesive force.The concentrations of Eudragit® fall within a range of 5-10 wt.-%,relative to the granulate. Lower concentrations of Eudragit® do notcreate the desired granulates because of the limited force of adhesion,i.e. the proportion of fines would be too large to achieve the desiredeffect.

According to the invention, a granulate made from at least one part ofthe formulation constituents of the polyelectrolyte cement present insolid form is provided. In this context of an autogenous granulation, atleast one part of the reaction partner (b) serves as the essentialgranulation agent, and the granulate breaks down again on contact withthe liquid formulation constituents into the primary grain, so that theliquid and solid components of the polyelectrolyte cement can easily bemixed internally with one another by the introduction of mechanicalenergy.

Mechanical energy can be introduced in various ways. For example, in thecase of hand mixed variants, energy is introduced via the spatula; inthe case of single application capsules, energy is introduced by shakingthe capsule in an automatic mixing device.

The advantages of the embodiment according to the invention include areduced mixing time for the polyelectrolyte cements according to theinvention. This leads to a shortening of the mixing time ofpolyelectrolyte cements packed in single application capsules incommercially available automatic mixing systems and to a significantsimplification of mixing with so-called ‘hand-mixing variants’ of thepolyelectrolyte cement according to the invention in a granular form ofpresentation.

Within the sense of the present invention, “autogenous granulation”should be understood to mean that the granulation takes place withoutthe additional use of granulation excipients. On the contrary, thepolyelectrolyte which is at least partially present in the powdermixture acts as a granulation excipient.

Surprisingly, two actually mutually reactive substances can begranulated in this manner, without a reaction being triggered betweenthem. The granulate according to the invention is thereforecharacterized in that no significant quantities of granulation excipientare used in production and therefore that the granulate contains nosignificant amounts of conventional granulation agents.

The granulate is mixed with the liquid to trigger the curing reaction.Because of the very rapid absorption of water through the capillaries ofthe granulate, the granulate is destroyed apart from the primary grain,so that small film thicknesses are guaranteed. The liquid is absorbedleading to ease of mixing.

For dental applications, the granulate according to the inventionpreferably provides a mean particle size between 10 and 1000 μmparticularly preferably between 50 and 500 μm.

Several known processes for producing granulates are described in thestate of the art (see e.g. [Ullmanns Encyklopädie der technischenChemie, Weinheim, 4^(th) edition, 1979, 18-157 ff]). Current processesin this context are wet granulation, fusion granulation and drygranulation. These processes are essentially suitable for producing thegranulate according to the invention.

Implementation of a wet granulation is particularly preferred with asolvent or a solvent mixture which partially dissolves at least a partof reaction partner (b) without triggering a reaction between the tworeaction partners (a) and (b), and which is removed after granulation.Wet granulation produces particularly high levels of porosity, wherebythe mixing times can be favourably reduced. The addition of solventsduring granulation partially dissolves the polyacid thereby leading tothe formation of the granulate. The solvent in this context must beselected in such a manner that the polyacid is partially dissolved butthat no reaction is triggered. Particularly preferably, the solventsused for the wet granulation provide polar properties. Very particularlypreferably, the solvent mixture used provides primarily short-chainedalcohols. The granulation mixture is produced in mixers by the additionof solvents. The solvent is evaporated off after granulation.

Another preferred process for producing the granulate according to theinvention is by dry granulation. In this case, the substances to begranulated are compressed to form scabs by the introduction ofmechanical energy. These compressed forms are then destroyed in agrinder in a subsequent grinding stage. The resulting fragmentedgranulate is graded. The granules with a grain size outside the requiredlimits are again compressed to form scabs. The granules within therequired range of grain sizes are passed for packaging.

Within the context of the present invention, it has been shown that animprovement in storage stability can be achieved through granulationalone without preceding surface coating.

This affects single-component or multiple-component polyelectrolytecements containing at least two reaction partners, (a) at least onemetal-cation-releasing compound and (b) one or more polyelectrolyteswhich are capable of conversion into a solid state, wherein at least oneof the polyelectrolytes is at least partially water soluble, wherein—inthe context of an autogenous granulation—at least one part of thereaction partner (b) acts as an essential granulation excipient for thegranulation of at least one part of the formulation constituents of thepolyelectrolyte cement present in solid form.

The polyelectrolyte cements and granulates according to the inventioncan be used for the production of dental materials, in particular forthe production of filling materials, fastening materials, base-fillingmaterials, stump restructuring materials and supplementary materials (A.D. Wilson, J. W. McLean, Class Ionomer Cement, Quintessenz Verlags GmbH,Berlin 1998], endodontic materials, in particular for ortho- andretrograde filling (EP-C-04 69 573], fissure sealing materials [J. W.McLean, A. A. Wilson, Br Dent. J. 136, 269-276, 1974], orthodonticfastening materials [H. W. Seehozer, Schweiz. Monatsschr. Zahnmed. 97,344-347, 1987] or filling materials for open furcations [C. Hüskens, C.Matter-Grütter, F. Lutz, Schweiz. Monatsschr. Zahnmed. 105, 216-221,1995].

The polyelectrolyte cements and/or granulates of the invention arenormally packed in containers such as mixing capsules, cartridges, tubesand jars. Depending on the container which is used for packaging,different instruments are used for mixing and/or application.

EXAMPLES Surface Coating

The following exemplary embodiments describe various polyelectrolytecements according to the invention. Example 1 (comparison) was producedby analogy with the Examples 2-10 of the invention; Example 11(comparison) was produced by analogy with Example 12 according to theinvention without the addition of an organic surface coating agent.Example 12a also serves the purpose of comparison.

All of the examples use metal-cation-releasing compounds and liquidsfrom commercially available products (ESPE Dental AG). Ketac-Molar®powder contains a glass for glass ionomer cements and Durelon® powdercontains a ZnO for polycarboxylate cements.

The coating agents were pre-dissolved in the solvents indicated in thetable in order to coat the metal-cation-releasing compound. In eachcase, the concentration of the solvent was adjusted so that the powderwas wetted optimally by the solvent. After mixing the powder in alaboratory mixer, this was dried for approximately 3 hours atapproximately 100° C.

The powder was mixed, either without coating or after coating, with dryacid on the Rohn wheel for approximately 30 minutes. A copolymer madefrom acrylic and maleic acid (Ketac-Molar® liquid) was used in theexperiments with glass ionomer cements, while the experiments withpolycarboxylic cement used pure polyacrylic acid (Durelon® liquid). Thetype and concentration of coating agent (relative to themetal-cation-releasing compound) and the concentration of thepolyalkenoic acid in the final mixture are shown in Table 1.

To measure the curing process, the two reaction partners present insolid form and homogeneously mixed—the metal-cation-releasing compoundand the polyelectrolyte—were mixed in the powder/liquid (P/L) ratioindicated with the liquid shown in Table 1 and curing was measured witha rheometer of the Curometer type (Shawberry). The values shown in thetable relate to the start of curring (t₃). Table 2 and FIGS. 1-3represent the course of curing during storage with 50% relative humidityat 23° C.

The Eudragit® E tartrate was produced by neutralization of 45 gEudragit® E with 11 g tartaric acid in aqueous solution.

Example 12a (Comparison)

A mixture of 95% Ketac-Molar glass powder and 5% Eudragit E tartrate wascured with Ketac-Molar liquid. Because of the strong thickening of thecement mixture, it is only possible to select a powder-liquid ratio of2.4. The mechanical properties listed in Table 3 show a clear declineboth by comparison with the reference cement and also by comparison witha cement which has been coated within the concentration range accordingto the invention:

TABLE 1 Experimental conditions Metal- Polyelectrolyte in cation Coatingagent powder mixture releasing Conc. Conc. P/L Example no. compound Type[%] Solvent Type [%] Liquid [g/g] 1 Ketac- — 0 — Copolymer 5 Ketac- 3,4(comparison) Molar ® Molar ® 2 Ketac- Eudragit ® 0.5 i- Copolymer 5Ketac- 3,4 Molar ® E propanol Molar ® 3 Ketac- Eudragit ® 0.5 acetoneCopolymer 5 Ketac- 3,4 Molar ® E Molar ® 4 Ketac- Eudragit ® 0.2 acetoneCopolymer 5 Ketac- 3,4 Molar ® E Molar ® 5 Ketac- Eudragit ® 1.24 waterCopolymer 5 Ketac- 3,4 Molar ® E tartrate Molar ® 6 Ketac- Eudragit ®0.25 water Copolymer 5 Ketac- 3,4 Molar ® E tartrate Molar ® 7 Ketac-Eudragit ® 0.62 water Copolymer 5 Ketac- 3,4 Molar ® E tartrate Molar ®8 Ketac- Copolymer 0.5 water Copolymer 5 Ketac- 3,2 Molar ® 845-ISPMolar ® 9 Ketac- OPADRY ® 0.5 water Copolymer 5 Ketac- 3,4 Molar ® IIColorcon Molar ® 10 Ketac- Surelease 0.5 water Copolymer 5 Ketac- 3,4Molar ® - Colorcon Molar ® 11 Durelon ® — 0 — Polyacrylic 18 Durelon ®3,2 (comparison) acid 12 Durelon ® Eudragit ® 0.5 i- Polyacrylic 18Durelon ® 3,2 E propanol acid

TABLE 2 Experimental results (start of curing t₃ in min:sec) ExampleStarting Storage time [weeks] Storage time [months] no. value 1 2 1 2 31 1:40 1:55 2:05 2:20 2:50 3:00 (comparison 2 2:10 2:05 2:15 2:10 2:052:05 3 2:50 2:50 2:50 2:50 2:75 4 2:10 2:05 2:00 2:15 2:12 5 6:10 6:106:10 5:55 6 2:10 2:15 2:10 7 4:10 4:00 3:55 4:00 4:00 8 1:50 1:40 1:402:00 2:00 9 2:00 2:00 2:05 2:00 2:00 10 1:40 1:45 1:45 2:10 2:00 2:00 114:30 4:45 5:15 5:55 6:05 (comparison) 12 4:05 4:10 4:10 4:15 4:10 4:00

The results of these experiments show that the polyelectrolyte cementsaccording to the invention from Examples 2-10 and 12 provide anexcellent storage stability within the framework of the measuringaccuracy of the method (+/−15 sec), while the two comparison examplesshow a marked increase in the curing time even after 4 weeks, whichcontinues during further storage.

Moreover, the following Table 3 shows, by way of example, that, forinstance, in the case of Example 6 according to the invention bycomparison with Example 1 (comparison), the mechanical values have notbeen negatively influenced by the surface coating agent. The test bodiesrequired for measuring the compression strength and bending strengthwere measured in mPa in accordance with the standard ISO 997 or inaccordance with an ESPE internal standard based on ISO 4049. By way ofdeviation from ISO 4049 (test bodies with dimensions 15*2*2 mm) a testbody with dimensions 12*2*2 mm was used.

TABLE 3 Compression strength and bending strength of Example 6 bycomparison with Example 1 (standard deviations in brackets). Compressionstrength Bending strength [mPa] [mPa] Example 1 (comparison) 224 (20) 53(12) Example 6 248 (21) 56 (9)  Example 12a 147 (17) 25 (7) (comparison)

The results from these experiments show, that an improved storagestability is achieved with the polyelectrolyte cements according to theinvention without the surface coating agent exerting a negativeinfluence on the mechanical values by comparison with a referencematerial which had not been surface coated.

Granulation

Example 13

An autogenously granulated powder mixture was prepared from 18 partspolyacid and 100 parts glass powder, surface coated as in Example 7, byadding 12 parts isopropanol and homogenizing in a pharmaceutical mixerfor a few minutes. In order to set the required grain-size range, themoist mixture was then sieved over a sieve with a mesh size of 300 to500 μm. The solvent was removed by subsequent drying for approximatelytwo hours at 100° C.

Example 14 (Comparison)

Powder mixture as for Example 13 according to the invention, but surfacecoating and granulation were not carried out.

To test the physical properties of the polyelectrolyte cements accordingto standard ISO 9917 obtained in accordance with Examples 13 and 14,powder and liquid (water with 17 wt.-% tartaric acid) was mixed in aratio of 3.8. Table 4 compares selected physical properties of thepolyelectrolyte cement in accordance with Example 13 of the inventionwith the corresponding polyelectrolyte cements in accordance withExample 14 (comparison) and the following Example 15 (comparison).

TABLE 4 Physical properties of the polyelectrolyte cement obtained fromthe granulate of Example 13 according to the invention by comparisonwith polyelectrolyte cements obtained from Example 14 (comparison) and15 (comparison). Example 14 Example 15 Example 13 (comparison)(comparison) Compression 127 145 45 strength [mPa] Surface hardness 8151 22 [mPa] Film thickness [μm] 13 10 134

The non-granulated mixture (Example 14 (comparison)) showed signs ofde-mixing during storage in the glass jar, so that the product had to beshaken before use. In this context, a considerable evolution of dustoccurred so that the work surface often became contaminated with thepowder on removal. Mixing the powder with the liquid was only possiblewith an increased input of mechanical energy.

By contrast, the granulate (Example 13 of the invention) shows no signsof de-mixing in the glass jar. The granulate does not evolve dust; itcan be removed from the jar cleanly and measured very well. Duringmixing, it was quickly wetted and produced a very thin film. Thegranulated polyelectrolyte cement fulfils all requirements.

Moreover, the mixing times for powders obtainable from Example 13 and 14(comparison) with water (water with 17 wt.-% tartaric acid) wereinvestigated. To this end, 380 mg powder and 100 mg liquid were weighedin each case onto a mixing block. The measuring time began when thedroplet of liquid came into contact with the powder and ended when ahomogeneous cement without pockets of powder had been obtained. The datameasured are presented in Table 5.

TABLE 5 mixing times Example 13 mixing Example 14 mixing time Mixingexperiment no. time [sec] (comparison) [sec] 1 12 32 2 11 35 3 13 34 410 28 5 12 38 6 10 32 7 11 34 8 14 29 9 10 29 10 10 34 Mean value 11.3(1.3) 32.5 (3.0) (standard deviation)

The results from these experiments show that the granulates according tothe invention provide clearly reduced mixing times to obtain ahomogeneously mixed polyelectrolyte cement (time reduction of more than60%). This is attributable to the considerably improved wetting of thegranulates with liquid by comparison with Example 14 (comparison).

Example 15 (Comparison)

The powder mixture from Example 14 (comparison) was placed in apharmaceutical mixer and granulated with 5% Eudragit® E relative to thegranulated powder mixture. A sieve of mesh width 300 to 500 μm was usedto obtain the required grain size by analogy with Example 13 of theinvention. The solvent was removed again by drying at 100° C. Thegranulated powder was mixed as described for Example 13 and 14, and theresulting polyelectrolyte cement was tested. The data obtained are shownin Table 4.

The comparison with non-surface-treated and non-granulated powder fromExample 14 (comparison) shows that even the recommended minimum amountof approx. 5% granulation excipient (see above) relative to thegranulated powder mixture severely worsens the physical properties ofthe polyelectrolyte cement. This shows that the use of currentlyavailable granulation excipients is not appropriate for production ofthe granulates according to the invention.

What is claimed is:
 1. A single-component or multiple-componentpolyelectrolyte cement comprising at least two reaction elements: (a) atleast one metal-cation-releasing compound and (b) one or morepolyelectrolytes capable of being converted into a solid state, whereinat least one of the polyelectrolytes is at least partially watersoluble, and wherein at least a part of reaction element (a) and/or (b)is at least partially coated with an organic surface-coating agent,wherein the organic surface-coating agent is a film-forming material andis present in a quantity from 0.01 to 3 wt.-% relative to thetotal-weight of the surface-coated material.
 2. The polyelectrolytecement according to claim 1, wherein the two reaction elements (a) and(b) are contained at least partially within the same component of thepolyelectrolyte cement.
 3. The polyelectrolyte cement according to claim1, wherein at least a part of the reaction elements (a) and/or (b)contained within the same component is coated with an organicsurface-coating agent.
 4. The polyelectrolyte cement according to claim1, wherein the organic surface-coating agent is at least partiallysoluble in acid.
 5. The polyelectrolyte cement according to claim 1,wherein at least a part of the component present in solid form ispresent in powdered, granulated and/or tablet form.
 6. A process forproduction of a polyelectrolyte cement comprising the steps of: (a)providing at least one metal-cation-releasing compound and one or morepolyelectrolytes capable of being converted into a solid state, whereinat least one of the polyelectrolytes is at least partially water solubleand acts as an essential granulation agent, and (b) at least partiallycovering a component to be granulated with the granulation agent.
 7. Theprocess according to claim 6, wherein step (b) is implemented as a wetgranulation with a solvent or a solvent mixture, which dissolves atleast a part of the polyelectrolytes without triggering a reactionbetween the metal-cation-releasing compound and polyelectrolytes, andwhich is removed after granulation.
 8. The process according to any oneof claims 6 to 7, wherein the solvents used for wet granulation providepolar properties.
 9. The process according to claim 6, wherein step (b)occurs as a dry granulation.
 10. A granulate obtainable through theprocess according to claim
 6. 11. The granulate according to claim 10,which provides a mean grain size between 10 and 1000 μm.
 12. A dentalmaterial comprising the polyelectrolyte cement according to any one ofclaims 1 to 5 and/or a granulate according to any one of claims 10 to11.
 13. A container comprising a polyelectrolyte cement according to anyone of claims 1 to 5 and/or a granulate according to any one of claims10 to
 11. 14. An application device comprising a polyelectrolyte cementaccording to any one of claims 1 to 5 and/or a granulate according toany one of claims 10 to 11.